Printing apparatus used for electronic computers

ABSTRACT

A printing apparatus used for electronic computers, comprises a plurality of type wheels mounted in juxtaposition on a shaft, a corresponding plurality of rotatable type selecting members arranged also in juxtaposition and in mesh engagement with said type wheels, respectively, said type selecting members carrying respective engaging members, and a common operation member in engagement with said engaging members, in such a manner that through rotational movement of said operation member the type selecting members are caused to be rotated to attain simultaneous drive of said type wheels. The type selecting members are adapted to be stopped by respective selector means when the types on the type wheels are located in registration with the printing positions, and upon completion of the selection of all the types desired, a printing hammer is actuated to print them on a paper medium.

United States Patent [191 Okawara et al.

[ NOV.5, 1974 PRINTING APPARATUS USED FOR ELECTRONIC COMPUTERS [73] Assignee: Citizen Tokei Company Limited,

Tokyo, Japan [22] Filed: Dec. 18, 1972 [21] Appl. No.: 316,215

[30] Foreign Application Priority Data UNITED STATES PATENTS 3,465,100 9/1969 Ricciardi et al 178/33 R Primary ExaminerThomas A. Robinson Attorney, Agent, or Firm-Elliott l. Pollock [5 7] ABSTRACT A printing apparatus used for electronic computers, comprises a plurality of type wheels mounted in juxtaposition on a shaft, a corresponding plurality of rotatable type selecting members arranged also in juxtaposition and in mesh engagement with said type wheels, respectively, said type selecting members carrying respective engaging members, and a common operation member in engagement with said engaging members, in such a manner that through rotational movement of said operation member the type selecting members are caused to be rotated to attain simultaneous drive of said type wheels. The type selecting members are adapted to be stopped by respective selector means when the types on the type wheels are located in registration with the printing positions, and upon completion of the selection of all the types desired, a printing hammer is actuated to print them on a paper medium.

2 Claims, 4 Drawing Figures PRINTING APPARATUS USED FOR ELECTRONIC COMPUTERS This invention relates to an improved construction of a drive mechanism for a numeral or letter character selecting member to be incorporated in a printing apparatus, more particularly a printing apparatus which is conveniently used, in associated with an electronic computer, to record through printing the data or output signals issued from it on a ledger or slip.

In conventional printing apparatuses wherein selected types are printed all at one time, it is a common practice to employ an operation member which is permanently connected, through elastic means such as biasing springs, to printing-type carrying wheels or sectors in mesh-engagement with the type wheels. These prior art printing apparatuses, however, have exhibited the problem that even after the type wheels had stopped their motions of rotation with desired numbers or letters to be printed having been selected, the operation member still continued its motion thereby imposing further load on the springs and subjecting the drive source of the apparatus to severe loading conditions. This results in the necessity of employing a comparatively bulky drive source. Besides, due to the fact that the springs have to be large-sized enough to extend to the lengths necessary to locate all the printing-types at the printing positions, the conventional structures have been also had the disadvantage that the overall size of the apparatus, especially as measured in the direction of the juxtaposed type wheels, is necessarily increased. For the reasons described above, accordingly, it has been impracticable with the prior art printing apparatus to print relatively larger printing types arranged side-by-side on rather a limited entry area of the ledger or slip.

The first object of the invention, therefore, is to improve the above described prior art by providing a compact printing apparatus in which type selecting members (number or character selecting members) in operative association with corresponding type wheels are adapted to disengage from an operation member when said type selecting members are arrested in selected positions by the action of associated selector means, with the resultant effect of allowing the use of small-sized spring elements, and which makes it possible to print a relatively larger number of types in a limited entry area of the ledger or slip.

The second object of the invention is to provide a printing apparatus of the type described which makes it possible to avoid the reverse movement of the type selecting member due to the reaction occurring when the type selecting member is disconnected from the operation member.

The third object of the invention is to provide a printing apparatus of the type described which makes it possible to prevent misprints due to the undesirable rebound motion of the selector member which might possibly occur in the engagement of the selector member with the type selecting member, whereby type selecting errors in the selecting stage caused by rebound motion are prevented.

For better understanding of the invention, the invention will now be described in further detail with reference to one embodiment of the invention shown in the accompanying drawings, wherein:

FIG. 1 a perspective schematic view,'partly broken, of the printing apparatus according to the invention;

FIG. 2 is a side view showing the relative positions which the principal parts in the apparatus assume prior to the printing step;

FIG. 3 is a side view similar to FIG. 2 however showing how the principal parts are actuated upon movement of a clearing member; and

FIG. 4 is also a side view showing the relative positions which the parts assume when the printing process is effected.

- Referring to FIG. 1, reference numeral 1 indicates a driving cam fixed on the cam shaft 2 which is rotalably supported on the side frame walls enclosing the printing mechanism. This cam l is driven from a drive motor via a clutch (both are now shown), in such a manner that through its full rotation, one cycle of printing operation is achieved. Reference numeral 3 indicates a sector gear having two followers 4, 4' in rotary contact with the cam face la, which sector gear 3 is rotatable around a pivot 5 (fixed on the frame walls 50) by the motion of the cam 1, within a predetermined extent of angle. A pinion 6 is secured on a shaft 7 which is rotatably supported by the side walls of the frame,

and this pinion 6 is driven by the sector gear 3 in meshing engagement with it.

On the above described shaft 7, are provided two identical crank arm members 8 and 8' secured respectively adjacent opposing ends of the shaft. These two spaced arm members 8 and 8' carry an operation bar member 9 which extends parallel to the shaft 7. Thus, as the shaft 7 rotates reciprocally, the operation bar member 9 together with the crank arms 8 and 8' are caused to reciprocably rotate around the shaft 7. Refer ences 10 indicate a plurality of disk-like type selecting members arranged side-by-side and rotatable on the shaft 7. Each type selecting member 10 is portially formed with driving teeth 10a and a ratchet portion 10b around its periphery, and also defines an interior arcuate slot 10c. The aforesaid operation bar member 9 extends through the slots 10c of the several type selecting members 10. On one side of each type selecting member 10, also, are provided a pivot pin 11 and a stopper pin 12 which, respectively, support an engaging member 13 for pivotable movement and limit such movement.

As shown in FIG. 2, each engaging member 13 is provided with a recess 13a having an inner curved surface 13a, a slide surface 13b and a slanting surface 130. A U-shaped spring 14 has one end anchored by a pin 15 on the type selecting member 10 and the other end of the spring 14 elastically bears against one end of the engaging member 13, so that said engaging member 13 is biased into contact with the operation bar'member 9.

Reference numerals l6 identify a corresponding plurality of type wheels arranged side-by-side, rotatable on a fixed shaft 17 extending between the opposite side walls 50, each type wheel 16 being in mesh engagement with a corresponding type selecting member. Each of said type wheels 16 is formed with a plurality of toothed faces 18 therearound, each face being provided with aprinting type for a numeral or letter character l9.

Referring again to FIG. 2, reference numeral 20 indicates a stopper provided on the frame 50 and serving to restrict rotational movement of each type selecting member 10. Reference numerals 21 indicate a corresponding plurality of fork-like selector members arranged side-by-side, rotatable on a shaft 22 mounted on the frame 50, with each selector member 21 being in opposition toa corresponding type selecting member and being biased counterclockwise around the shaft 22, as viewed in the drawings, by a spring 23. Each fork-like selector member 21 has a pawl 21a at one end directed toward the type selecting member 10 and a projection 21c adjacent the other end. A plurality of auxiliary selector members 24 are arranged side-byside, rotatable on a shaft'25 mounted on the frame 50, and in such a manner that each auxiliary selector member 24 is in opposition to a corresponding selector member 21. It is arranged, further, that by the provision of a biasing spring 26 connected at one end of each auxiliary selector member 24, the other end of said auxiliary selector member 24 bears upon one end portion 27b of a slit opening 27a formed on a holding member 27 and can selectively engage a recess 21d on the selector member 21. Said holding member 27 is in the shape of a tube having a corresponding number of slit openings formed on the semicircumference into which the respective auxiliary selector members 24 are inserted thereby preventing movement of the auxiliary selector members 24 in the axial direction. (See FIG. 1)

As shown in FIG. 1, two levers 28 and 28' are pivotably supported on the shaft 25, each lever being secured to one end of the holding member 27. These two levers 28 and 28' carry a spring anchoring plate 29 fixed therebetween, and plate 29 holds one end of each aforesaid spring 26. Thus, the arrangement is such that when the levers 28 and 28' are rotated, the holding member 27 together with the spring anchoring plate 29 are caused for to rotationaly move around the shaft 25 en bloc. Further, the lever 28 is connected to a tension spring 30 which has its remote end fixed to a stud 48 mounted on the frame 50, so that the levers 28 and 28 are biased clockwise, as viewed on the drawings, to urge their lower ends 28a toward engagement with a clearing bar member 31.

A corresponding plurality of electromagnets 33 are provided side-by-side on a magnet mounting plate 32 fixed on the frame 50. Above these electromagnets, are provided a, corresponding plurality of channel-shaped retainer levers also arranged side-by-side in corresponding opposition to the respective electromagnets 33 and swingable around a shaft 34 fixed on the frame 50. Each retainer lever 35 has a roller 36 at its inner end and is normally biased by a spring 37 connected to its outer end so that the retainer levers 35 tend to rotate around the shaft 34 in the clockwise direction, as viewed on the drawings, to keep contact with a stopper plate 38 mounted on the frame 50. Numerals 39 indicate armature pieces each of which is secured on the lower surface of the respective retainer lever 35, whicharmature pieces 39 are attached toward the associated electromagnets 33 upon electromagnetical activation of the latter, to cause the retainer levers 35 to swing counterclockwise against the biasing forces of the springs 37 when the electromagnets 33 are energized.

Referring to FIG. 1, a type-position detector disk 40 made of suitable opaque material is fixed on the shaft 7, and this detector disk 40 has a plurality of throughholes 40a arranged radially in equally spaced relation to one another. Reference numeral 41 indicates a source of light located adjacent one side of disk 40 and 42 indicates a photoelectric sensor such as a photocell located on the other side of disk 40 and aligned with the light source. When the holes 40a rotating in synchronization with the type wheels 16 cross the axis of light the beam, respective signals for the printing type on each type wheel which are in registration with the printing position are sent from the photocell 42.

In FIG. 2, reference numeral 43 identifies an index member which is adapted to be selectively thrust, by an unillustrated drive means, into and between the adjacent teeth 18 on each type wheel 16 when the necessary operation of selecting the types is completed and the apparatus is ready for the printing step, thereby correcting any errors in the alignment of the types at the printing positions. 44 shows an ink ribbon, 45 a blank paper for printing, 46 a printing hammer, and 47 shows a support plate for the blank paper.

Now the operation of the printing apparatus of the invention will be described. For the sake of simplicity, the following description will refer only to the combination of associated parts such as the type wheels, selecting members, selector members, etc., unless otherwise required.

Upon completion of the storage of numerical and/or alphabetic necessarydata in an electronic computer, which data is to be printed out by the printing apparatus of the present invention in multiple figures or letter data, an operation key (not shown) provided in the apparatus is depressed to start the operation of the drive mechanism including the cam 1. As the cam 1 rotates,

the clearing bar member 31 is caused to move in the direction of the arrow A in FIG. 2 by the action of another cam (not shown) secured on the shaft 2 so that the clearing bar 31 engages the lower ends 28a of the levers 28 and 28' to rotate the levers counterclockwise against the force of the tension spring 30. Since the holding member 27 rotates together with the levers 28 and 28, the auxiliary selector members 24 are rotated counterclockwise under the biasing forces of the respective springs 26. However, each auxiliary selector member will be stopped from further rotational movement when it comes in contact with the portion immediately above the recess 21d of the respective fork-like selector member 21, and then remains immovable while still under the counterclockwise acting bias of the respective spring 26, as shown in FIG. 3.

As the clearing bar 31 moves in the arrow-indicated direction A, the lower end 21b of the selector member 21 disengages from the clearing bar 31, as shown in FIG. 3, while the projection 21c of the selector member 21 comes into engagement with the roller 36 of the retainer lever 35 so that said selector member 21 may be prevented from further counterclockwise rotation under the action of the respective spring 23.

Subsequently, when the cam follower 4 rides on the threshold of the increment formed on the cam 1, as shown in FIG. 1, the sector 3 which has been in the rest position, is driven in the clockwise direction, as viewed on the drawings, to cause the gear 6 and the shaft 7 to be rotated counterclockwise. Consequently, the crank arm members 8 and 8' and accordingly the operation bar member 9 integral therewith are rotated. As the operation bar member 9 is in frictional engagement with the engaging member 13 mounted on the side of the respective selecting member 10, under the biasing force of the respective U-shaped spring 14, all of the type selecting members are rotationally driven simultaneously following rotational movement of the operation bar member 9. This causes similar rotational movement of the type wheels 16 in mesh engagement with the respective selecting members 10. Similarly, the type-position detector disk 40 also rotates to permit the light beam from the source 41 to pass through the holes 40a on the detector disk 40 intermittently at intervals corresponding to those of the type carrying faces on each type-wheel 16. Thus, the photocell 42 generates intermittent signals successively identifying the types 19 which are in registration with the printing position. Then, by comparing the thus obtained signals with information previously stored in the memory of the electronic computer, it is possible at each detecting time to identify which type wheels are correctly selected or are ready to print the proper individual numbers at the appropriate numerical figure positions. Upon identification of the properly registered type wheels, the corresponding electromagnets 33 only are energized to attract the associated armature pieces 39. This causes the associated retainer levers 35 to be rotated counterclockwise, as shown in FIG. 4, against the force of the biasing springs 37, so that the rollers 36 on the retainer levers 35 roll downwardly on the associated projections 216 of the selector members 21 to release them from engagement with the projections 21c. Accordingly, the associated selector members 21 are caused to rotate counterclockwise by the action of the springs 23, so that the pawl 21a of each selector member 21 meshes with a particular tooth of ratchet portion 10b, corresponding to the selected type 19 which is then located at the printing position, whereby the type selecting member 10 is firmly held against any further rotational movement.

It is to be noted that when the selector member 21 rotates, the associated auxiliary selector member 24 also rotates keeping contact with the selector member 21 until the inner end of the auxiliary member 24 enters the recess 21d of the associated selector 21. Accordingly, any tendency of each selecting member 10 to move in a'reverse direction, that might occur from the momentary impact force exerted by the pawl 21a of the associated selector 21, can bedecreased or eliminated by the counteraction of the auxiliary selector 24. In other words and-more specifically,after hitting the inclined face of a ratchet tooth 10b, the pawl 21a is thereafter prevented from moving outwardly of the top of the tooth and is, instead, eventually forced to the bottom of the tooth, to attain a tight engagement between the selector 21 and the associated type selecting member 10 under all circumstances.

The operation bar member 9 still continues its rota- I tional movement during the above operation of selecting the types, and when the selecting member 10 is arrested by the associated selector, bar member 9 urges the surface 13a in the recess 13a of the associated engaging member 13, in the upper direction, against the biasing U-shaped spring 14, thereby releasing engagement between it and the engaging member 13. Subsequently, the operation bar member 9 is forced to move along the slide surface 1312 until it is completely disengaged from the engaging member 13 and continues its rotational movement, while the type selecting member 10 and the type wheel 16 are left at their rest positions.

It is to be noted that, due to the provision of the slide surface 13b with which the operation bar member 9 frictionally engages, it is made possible to avoid reverse rotation of the type selecting member 10 due to any reaction occurring when the member 9 disengages from the recess 13a because, even after said operation bar member 9 is disengaged from the recess 13a of the engaging member 13, the member 9 slides on the slide surface 13b in frictional contact with said surface prior to its complete disengagement from the engaging member 13. Therefore, the type selecting member 10 is driven continuously by the engaging member 13 until the member 9 is completely disengaged from the engaging member 13. Even if the type selecting member 10 were to have a slight tendency to reverse its direction of movement, the engaging member 13 would still be moved by the frictional engagement with the member 9 until the pawl 21a of the selector member 20 engages deeply with the ratchet 1012, thereby preventing reverse rotation of the type selecting member 10. As a result, all the types 19 on the type wheels 16 set as the respective printing positions are arranged in alignment whereby the functioning of the index member. 43 is greatly facilitated so as to assure a satisfactory printing result. In addition, due, to the fact that the impact occuring the moment the operation bar member 9 is completely disengaged from the engaging member 13 can be alleviated, as previously described, it is possible to attain stability in rotational movement of the typeposition detector disk 40 (See FIG. 1), thereby warranting a high-accuracy signalling operation without errors in the selection of type to be printed.

In the manner described above, any other types on the type wheels which have not yet been selected, will be selected and set at the respective printing positions during the rotational movement of the operation bar member, the total possible angular displacement of bar member 9 being enough to enable all the types on the type wheels to be placed at the respective printing positions. When the operation bar member 9 is stopped by the action of the cam 1, the index member 43 is actuated by a further cam (not shown) secured on the cam shaft 2 to cause member 43 to be inserted into and between the adjoining tooth 18 on each type wheel 16, thus further improving alignment of the complete set of types placed at the printing positions. This index member 43, in any event, does not strike the type carrying faces on the type wheels since the selecting member 10 stops at a right position and its associated type wheel 16 also stops substantially at a right position, as described previously. Thereafter, the printing hammer 46 is actuated to effect printing the types in a set arrange ment all at one time.

Upon completion of the printing step, the clearing bar 31 is caused to move in the direction of the arrow B in FIG. 4 and the levers 28 and 28' are rotated clockwise by the action of the tension springs 30 so that the inner ends 27b of the slit openings 27a on the holding member 27 come into engagement with the respective auxiliary selectors 24. Since the spring anchoring plate 29 also rotates with the levers 28 and 28', the springs 26 flex less so that the auxiliary selectors 24 can easily be rotated back in the clockwise direction.

After the auxiliary selector 24 is urged by the end 27b of the slit opening 27a on the holding member '27 to part from the recess 21d of the selector 21, the clearing bar member 31 still continues its movement in the arrow-indicated direction B until it comes into contact with the lower end 21b of the selector member 21. This causes the selector member 21 to rotate clockwise, against the biasing force of the spring 23, to disengage from the type selecting member 10. Also, as the selector 21 rotates clockwise, its projection 21c moves out of engagement with the roller 36 of the retainer lever 35 so thatthe retainer lever 35 returns to its original position shown in FIG. 2.

Thereafter, as the cam 1 further progresses, the operation bar member 9 starts rotational movement in the opposite or clockwise direction along the arcuate slot 100 on the type selecting member 10, and comes into engagement with the slanting surface 13c on the engaging member 13 being subjected to a counterclockwise bias by the U-shaped spring 14, thereby causing the type selecting member 10, which has been at rest, to be rotated clockwise until its step portion 10d is caught by the stopper 20. With further rotational movement of said operation bar 9, the operation bar 9 urges the slanting surface 13c on the engaging member 13 in the upward direction against the biasing force of the U- shaped spring 14, and eventually comes into fit engagement with the recess 13a on the engaging member 13, thus ceasing its movement.

In this manner, all of the type selecting members 10 and type wheels 16 are returned to their original positions while the cam shaft 2 is disconnected from the drive motor by the action of the aforementioned clutch, and takes the original position. One cycle of the printing operation has now been completed.

Although the invention has been so far described by reference to the one preferred form of structure which is illustrated in the drawings, the invention is in no way limited to the illustrated example chosen for the purpose of disclosure, and can be practiced in various other ways. For example, two of the associated members, the type selector and type wheel, can be formed as one body by modifying the former such that necessary printing types are provided on the teeth; or instead of the illustrated structure of the type selecting member and the operation bar member, it may be possible to use type selecting members as rectangular shape adapted for linear reciprocal movement and cooperating with operation bar members adapted also for linear reciprocal movement. Though in .the described embodiment it is arranged that one cycle of the printing operation is completed by the forward and return strokes of the operation bar member, the process of selecting the types being carried out in the forward stroke of the operation bar while in the return stroke after printing the operation bar is brought to the initial engagement with the engaging member, an alternative arrangement may be practiced wherein the cyclic operation of printing is started at the beginning of the backward stroke of the operation bar member, including restoration of engagement between the operation bar member and the engaging member effected in the return stroke of the bar member and selecting the necessary types effected in the forward stroke of the operation bar member, and ends in the printing step.

Further, though in the described practice, the forklike selector member provides the recess thereon which is adapted for engagement with the associated auxiliary selector member upon rotation of the selector member to a certain extent so that the selector member is restrained against moving over a predetermined distance in the reverse direction, it is alternatively possible that without employment of such recesses on the selector member, both the selector and auxiliary selector engage each other in a suitable form of relative engagement with such selected frictional angles that when the selector tends to move in a reverse direction, the component force of the friction works in that direction to attain an increasingly tight engagement of the auxiliary selector with the selector member.

As apparent from the foregoing, the present invention offers the following advantages:

1. Upon completion of the type selection or stopping of the type selecting member, the operation bar member moves along the slide surface provided on the engaging member and then disengages from the engaging member. This results in a very smooth, satisfactory manner of accomplishing disengagement between the two members without any adverse effect on other associated parts in the printing apparatus. Thus, it is possible to produce printing of superior quality.

2. Also, due to the fact that the operation bar member is adapted for complete disengagement from the engaging member only after the bar member has passed along the slide surface of the engaging member, as mentioned above, it is possible to reduce the rate of load fluctuation imposed on the prime mover, hence permitting the use of a relatively smaller-sized prime mover for the printing apparatus.

3. Because of no provision being made for springs connecting between the operation bar member and each'type selecting member, the prior art necessity of employing large-sized springs can be avoided in the invention.

Thus, the invention provides a printing apparatus which makes it possible to print relatively larger-sized numerals or letters in multiple figures or columns upon a rather limited entry area of the ledger or slip.

According to the invention, still further, since the provision of the auxiliary selector member adapted for engagement with the selector member prevents rebounds of the selector member that might otherwise occur the moment the selector engages the type selecting member, it will never occur that the pawl of the selector member erroneously engages any ratchet teeth other than the selected ratchet tooth. Therefore, it is possible to provide ratchet teeth having sufficient strength without specially designing the tooth configuration. Thus, there can be obtained a printing apparatus equipped with reliable selecting means.

Further, with the arrangement according 'to the invention wherein an anchoring plate for the springs biasing the corresponding auxiliary selectors is provided for rotational movement, it is advantageous that when the selector is actuated, the associated auxiliary selector can be firmly engaged while the biasing force to the auxiliary selector is alleviated when the auxiliary selector is disengaged from the selector. This feature additionally helps in enhancing the effects described in the preceding paragraph.

We claim:

1. A printer comprising a plurality of typewheels mounted for rotation in side by side relation to one another; a plurality of movable type selecting members rotatably disposed on a shaft and in side by side relation to one another adjacent said typewheels respectively, each type selecting member having a ratchet portion formed as a part thereof, a toothed portion in driving engagement with one of said typewheels formed as another part thereof, and a slot; an operation bar member connected to said shaft for reciprocal motion, said operation bar member extending through said slots for driving said type selecting members; a plurality of engaging members pivotally mounted on said type selecting members respectively adjacent said slots, each engaging member having a recess positioned to frictionally engage said operation bar member when said operation bar member is disposed adjacent a particular portion of said slot, each engaging member also having a slide surface continuing from said recess and positioned to frictionally engage said operation bar member when said operation bar member is adjacent a different portion of said slot, each type selecting member having a spring member for urging said operation bar member into frictional engagement with said recess and continuing slide surface; a plurality of selector members adapted to stop rotation of said type selecting members respectively by engagement with associated ones of said ratchet portions; means for retracting said selector members away from said ratchet portions; and means for actuating said selector members to move said selector members from their retracted positions into engagement with said associated ratchet portions of said type selecting members when desired printing types on said typewheels are properly located in registration with the printing positions.

2. A printer according to claim 1 wherein said operation bar member comprises a rod extending generally parallel to said shaft for movement through an arc about said shaft, said slot in each type selecting member being of arcuate form, said slide surface extending along a portion of said engaging member on one side of its pivotal mounting and having an arcuate shape corresponding to the path of movement of said operation bar member; said spring meansbeing disposed on said type selecting member to engage said engaging member on the side of its pivotal mounting opposite to" arcuate slide surface.-

the portion having said 

1. A printer comprising a plurality of typewheels mounted for rotation in side by side relation to one another; a plurality of movable type selecting members rotatably disposed on a shaft and in side by side relation to one another adjacent said typewheels respectively, each type selecting member having a ratchet portion formed as a part thereof, a toothed portion in driving engagement with one of said typewheels formed as another part thereof, and a slot; an operation bar member connected to said shaft for reciprocal motion, said operation bar member extending through said slots for driving said type selecting members; a plurality of engaging members pivotally mounted on said type selecting members respectively adjacent said slots, each engaging member having a recess positioned to frictionally engage said operation bar member when said operation bar member is disposed adjacent a particular portion of said slot, each engaging member also having a slide surface continuing from said recess and positioned to frictionally engage said operation bar member when said operation bar member is adjacent a different portion of said slot, each type selecting member having a spring member for urging said operation bar member into frictional engagement with said recess and continuing slide surface; a plurality of selector members adapted to stop rotation of said type selecting members respectively by engagement with associated ones of said ratchet portions; means for retracting said selector members away from said ratchet portions; and means for actuating said selector members to move said selector members from their retracted positions into engagement with said associated ratchet portions of said type selecting members when desired printing types on said typewheels are properly located in registration with the printing positions.
 2. A printer according to claim 1 wherein said operation bar member comprises a rod extending generally parallel to said shaft for movement through an arc about said shaft, said slot in each type selecting member being of arcuate form, said slide surface extending along a portion of said engaging member on one side of its pivotal mounting and having an arcuate shape corresponding to the path of movement of said operation bar member; said spring means being disposed on said type selecting member to engage said engaging member on the side of its pivotal mounting opposite to the portion having said arcuate slide surface. 